This invention relates to changing the layer sequence of a coextrusion extrudate.
U.S. Pat. No. 4,839,131 to Cloeren and U.S. Pat. No. 5,102,323 to Blemberg disclose an exchangeable plug for changing the relative order of layers of an extrudate, in which the circumferential plug surface is provided with a plurality of channels. Under certain circumstances, leakage between plug channels can occur because of the mechanical clearance for plug removal. Reduction in the mechanical clearance can result in galling of the plug to the bore. Furthermore, manufacturing a tapered bore and a mating tapered plug with precise registering of channels, is an arduous task not practical in mass production.
Other approaches for changing the relative order of layers of an extrudate are illustrated by UK Patent Application No. 2,220,164 published January 1990, and U.S. Pat. Nos. 3,924,990, 4,443,397 and 4,483,669. The UK Application describes use of a set of distribution blocks interchangeably disposed between an entry block (or feed source) and a coextrusion block, and that an individual distribution block may comprise a stack of interchangeable plates. The U.S. Patents similarly describe changing the order of layers by exchanging apparatus disposed between rigidly connected feed pipes and a forming means shaping individual streams into a shape suitable for layering. However, a drawback of these approaches is that loosening or disconnecting feed pipes from the coextrusion apparatus, separation of feed sources from the forming means, and/or separation of the die body from the coextrusion apparatus is typically necessary for the exchange.
Accordingly, there is a need for a coextrusion apparatus which simplifies changing the relative order of layers of a coextruded extrudate.
In accordance with the present invention, there is provided a coextrusion apparatus which includes an interchangeably disposed device for selecting a relative order of layers in a combined stream. In fluid communication therewith, the apparatus further includes a channeled arrangement for suitably directing flow of a plurality of streams.
In a preferred embodiment, the interchangeably disposed, layer sequence selecting device is beneficially used in combination with a directing/combining assembly which includes a plurality of feed channels for directing feed streams to the layer sequence selecting device, and a plurality of connecting channels in fluid communication with, and for directing the streams from the layer sequence selecting device to, a downstream combining channel. The layer sequence selecting device includes a plurality of flow sequence selecting channels which register with the respective feed channels and connecting channels. An advantageous feature is that a feed channel exit opening is disposed relative to an entry opening of a respective connecting channel so that flow through the exit opening is in a direction generally opposite to the direction of flow through the entry opening.
In a second preferred embodiment, the interchangeably disposed, layer sequence selecting device is advantageously used in combination with a flow directing block and with an assembly for combining a plurality of streams and coextrusion of a multilayer extrudate which includes a combining channel and downstream thereof, an extrusion orifice. The flow directing block includes a plurality of feed channels for directing feed streams to the layer sequence selecting device, and a plurality of connecting channels in fluid communication with, and for directing the streams from the layer sequence selecting device to, the combining/extruding assembly. As before, the layer sequence selecting device includes a plurality of flow sequence selecting channels registering with the respective feed channels and connecting channels, and a feed channel exit opening is beneficially disposed relative to an entry opening of a respective connecting channel so that flow through the exit opening is in a direction generally opposite to the direction of flow through the entry opening.
Beneficially, an apparatus in accordance with the invention, provides for changing the relative order of layers of a coextrusion extrudate without disassembly of extrusion apparatus structure other than removal and interchanging of the layer sequence selecting device. In addition, such an apparatus avoids need for mechanical clearance as is necessary between a removable plug and its respective bore.
Additional advantages and beneficial features of the present invention are set forth in the drawing and detailed description, and in part will become apparent to those skilled in the art upon examination of the drawing and detailed description or may be learned by practice of the invention. In the drawing and detailed description, there are shown and essentially described only preferred embodiments of this invention, simply by way of illustration of the best mode contemplated of carrying out this invention. As will be realized, this invention is capable of other and different embodiments, and its several details are capable of modification in various respects, all without departing from the invention. Accordingly, the drawing and the detailed description are to be regarded as illustrative in nature, and not as restrictive.